With reference to FIGS. 1B and 17, common VTRs include a head cylinder 2 inclined at a specified angle and mounted on a cylinder base 1, and a pair of circular-arc rails 30a, 30b arranged around the head cylinder 2. Tape guide assemblies 50a, 50b are slidably mounted on the rails 30a, 30b, respectively. The guide assemblies 50a, 50b are moved along the respective rails to thereby withdraw magnetic tape 71 from a tape cassette 7 and wind the tape around the head cylinder 2 over a predetermined angle about the center thereof.
As shown in FIG. 24, the tape guide assembly 50a comprises guides 53, 54 provided on the upper side of a slide base 52 for withdrawing the tape, a rod 58 projecting from the lower side of the base 52 and extending through a guide slit 32 of the rail 30a, and a pair of slide pieces 101, 101 provided on the respective opposite sides of the slide base 52. Pulling drive means comprising a loading ring, etc. is connected to the lower end of the rod 58 by a connector as will be described later to exert on the guide assembly 50a a pulling force acting longitudinally of the guide slit 32 of the rail.
Usually, one of the pair of rails, 30b, is formed along a plane and disposed approximately horizontally above the cylinder base 1, whereas the other rail 30a is curved to include a bent portion R and inclined with respect to the cylinder base 1 (see, for example, Unexamined Japanese Patent Publications SHO 60-87458, SHO 59-171070 and SHO 60-35364). Accordingly, the guide assembly 50a on the curved rail 30a is held at the same level as the cassette 7 as indicated in solid line before starting to load the tape, gradually rises as it advances with a loading operation, and reaches a predetermined level as indicated in broken line on completion of the loading operation. At the higher level, the assembly 50a is held as inclined. As seen in FIG. 17, consequently, the magnetic tape 71 withdrawn from the cassette 7 is wound at a predetermined angle of inclination around the head cylinder 2.
With reference to FIG. 24, the guide assembly 50a at the end of path of its movement is positioned by the contact of the pair of slide pieces 101, 101 at opposite sides of the slide base 52 with the rail 30a with respect to the direction of Z axis shown (axial direction of the rod 58), and also by the contact of the rod 58 projecting downward from the slide base with the slit (32) defining side wall of the rail 30a with respect to the direction of X axis (perpendicular to the Z axis).
Further with the conventional VTR, the path of travel of the tape from a supply reel 72 to the head cylinder 2 when the tape is completely loaded as seen in FIG. 17 is provided by a tape drawing guide 63, first to third tape guides 9, 91, 92 and the pair of guides 53, 54, and all of these tape guides 63, 91, 92, 53, 54 other than the first tape guide 9 are mounted on a pivotal arm (not shown) operatively related to the loading movement. These movable guides advance with the loading movement and withdraw the magnetic tape 71 in sliding contact with the nonmagnetic side of the tape 71 to form the specified tape travel path.
With the conventional VTR wherein the supply rail 30a is curved and includes the bent portion R, the tape supply guide assembly 50a must have some play relative to the rail 30a. Consequently, the play causes a backlash. Especially with compact 8-mm VTRs wherein the rail 30a is spaced from the head cylinder 2 by a small distance, the guide assembly 50a is likely to come into contact with the head cylinder 2 during tape loading. To preclude the backlash, the portion where the guide assembly 50a is in engagement with the rail 30a requires complex means for absorbing the play.
Further in the arrangement of FIG. 24 for positioning the guide assembly 50a in place, the assembly is positioned with respect to the direction of X axis by the line contact between the periphery of the rod 58 and the guide slit (32) defining side wall of the rail 30a, so that owing to variations in the accuracy with which the guide slit 32 is machined, the rod 58 is likely to contact the upper edge of the slit defining wall or the lower edge thereof. This results in variations in the accuracy with which the guide assembly is positionable, making it difficult to position the assembly properly.
The conventional VTR has another problem in that the loading mechanism is very complex because the multiplicity of tape guides 63, 91, 92, 53, 54 need to be arranged movably as seen in FIG. 17 to provide the travel path for the tape as completely loaded and further because a link assembly is necessary for driving these guides forward and rearward.
These problems impose limitations on attempts to provide lightweight and compacted loading mechanisms for 8-mm VTRs.